Imagine being in a mental hospital where the nurses, psychiatrists and patients all speak a foreign language. In your frantic efforts to be understood you wave your hands and gesticulate wildly. You are labelled aggressive.

Years pass. You are given medication and kept locked up. Then you are sent somewhere where people speak your language. You explain your frustrations, understand what the psychiatrist says and in a few months are well enough to be discharged.

This nightmare scenario will be readily recognised by deaf psychiatric patients. There are only three units in Britain for deaf patients where the staff use sign language. The units - in London, Birmingham and Manchester - have all dealt with patients who have spent years locked away.

In one of them, a special unit for children should help to ensure they never have to suffer the desperate confusions of adult deaf mentally ill people.

The deaf unit at Springfield Hospital in Wandsworth, London, is unique in Britain in having a child psychiatrist for the deaf. Dr Peter Hindley sees about 60 children or adolescents a year. 'Most families with deaf children cope well, but deaf children have the full range of emotional and behaviour problems that hearing children might experience,' says Dr Hindley. 'Deaf children also experience anxiety and depression, but diagnosis is difficult if you are not skilled in sign language. The largest group we see have conduct problems like aggression. Lack of communication affects psychological and social development and, because communication is difficult, parents can be over-controlling.

'The simplest thing we do is to get families together, using an experienced sign language interpreter. Often it is their first opportunity of talking in a relaxed way,' says Dr Hindley.

Eight-year-old Carl was referred to the unit because of behaviour problems. His family was counselled and the school advised on behaviour management techniques. Over six months he showed a great improvement. His parents had an opportunity to talk about their feelings and his effect on their marriage. A deaf member of staff helped them to understand how Carl saw the world. They realised how confused he had been whenever he had seen his parents arguing because he couldn't understand what it was about.

In some families, deaf children are made scapegoats. 'They are blamed for everything and rejected by both parents and siblings,' says Dr Hindley. 'It is possible to change behaviour and attitudes through family therapy. But for some of our teenagers the best thing we can do is to help them separate from their families in the least painful way.'

Research shows deaf children suffer higher rates of physical and sexual abuse. They can be targeted by abusive adults because of their difficulty in reporting abuse.

Dr Hindley says: 'Adults always find it difficult to believe children who say they are being abused. It is harder if they are deaf. We are often the first to ask the children what they are thinking and feeling. Without good signing we wouldn't get to first base in terms of understanding their perception of the problem. Suddenly, hearing parents know what their child is saying.'

The children and adults at Springfield, and the other centres, are the lucky ones. Many deaf people are still housed in ordinary mental hospitals, becoming either increasingly disruptive or withdrawn. Hearing people tend to think the deaf should be able to communicate by writing. They don't realise that those born deaf or deafened in the first few years of life tend to have only a poor grasp of English. For many deaf people sign language is their only fluent language.

Psychiatrists used to believe that depression was uncommon in deaf people, who were instead prone to behaviour problems. Once the Springfield unit opened, the proportions of the psychiatric disorders dealt with changed dramatically. The figures for depression quadrupled while numbers suffering emotional problems doubled. The proportion of those suffering conduct disorder halved.

The unit opened in 1971, almost by accident, when a nurse with deaf parents and a consultant set up a day group. Other hospitals in the area demanded their troublesome deaf patients should be allowed to join. A study in 1972, commissioned by the Royal Association in Aid of Deaf People, emphasised the need for change. It showed that South West Thames had 10 times more deaf patients in mental hospitals than their population size would have indicated.

Sign language is the key. One third of Springfield's staff is deaf. One is a social worker, one a drama therapist and one training as a psycho-dynamic counsellor. The rest are in unqualified posts.

Herbert Marvin, 40, is a deaf advisor at Springfield. He has been deaf from birth and is married to a deaf wife. They have three hearing sons. He was working as a carpenter when he saw an advertisement for staff.

'I never thought I could become a professional mental health worker,' he says. 'In the past there were few opportunities for deaf people. I went to a deaf boarding school and had a good time with other deaf children. When I left I was dropped into a hearing world with no back-up.

'When I came here the patients had no experience of working with deaf staff. Seeing deaf staff gives them new role models. When patients arrive, their attitude to deafness is negative. But they watch how I behave and see me arguing with hearing people and it gives them confidence.'

Dr Nick Kitson, consultant psychiatrist and head of the unit, says: 'The health authority gave me nine months to learn sign language. I visited psychiatric units for deaf people in America and realised the importance of employing deaf people fluent in sign language. It is a very sophisticated language capable of expressing everything you can say in English.'

Deaf people who try to communicate in writing are quite often misunderstood. Experiments have shown that general psychiatrists cannot distinguish between the writings of a mentally ill person and those of a deaf person because most deaf people have a poor grammatical grasp of English.

Barry, a profoundly deaf man in his twenties, was sent to Rampton top security hospital after he attacked a passer-by. During the years he spent there his behaviour was explosively violent. In an attempt at rehabilitation, Barry was sent to Springfield. He was put in an open ward and found it difficult to cope with the freedom. At his own request he went back to Rampton for a period. Now he is back at Springfield, progressing steadily by working with a deaf member of staff who helps him to cope with violent impulses.

'He had communication problems and was rejected by his family.' says Dr Kitson. 'Being able to make himself understood made the difference to him. He didn't need psychiatric help but he did need fluent communication and psychological counselling.'